Linux ls命令解析

ls 指令可以说是Linux下最常用的指令之一。它有许多的选项，其中有许多是很有用的，你能否了解呢？下面列出了 ls 指令的绝大多数选项。

　　一运用举例：

　　1.列出具体文件 #ls -al //这个最常用，可是往往又不彻底符合要求，

　　2.列出一切子目录的文件：#ls -R  //上个指令仅仅列出了本目录下的一切目录和文件，可是目录下的文件不会循环的列出。

　　3.若是文件过多一屏看不完，怎么办？并且，关于想找到许多文件中的某个文件的姓名。

　　3.1分屏显现：#ls -l|more  //能在当时屏退出，很有用，但不能一页一页翻屏

　　#ls -l|less  //能用pgup，pgdw 翻页，但不能在当时方位退出

　　3.2横向输出竟能够多的显现文件姓名：#ls -m         

　　-a 列出目录下的一切文件，包含以 . 最初的隐含文件。//常用    　

　　-m 横向输出文件名，并以“，”作分格符。

　　-c 输出文件的 i 节点的修正时刻，并以此排序。

　　-R 列出一切子目录下的文件。

　　-l 列出文件的具体信息。

　　-s 在每个文件名后输出该文件的巨细。

　　-k 以 k 字节的方式表明文件的巨细。

　　-i 输出文件的 i 节点的索引信息。

　　2.只显现目录：#ls -l |grep ^d     只显现非目录文件：#ls-l |grep ^[^d]

　　3.对输出文件进行各种排序；

　　3.1 依照字符序(default): #ls -l

　　3.2 依照修正时刻排序： #ls -t  //近来修正在最上面

　　3.3 逆排序         ： #ls -r

　　3.4 按文件巨细排序  ：#ls -S  //大文件的在上

　　3.5 依照文件扩展名（最终一个.后的字符）排序： #ls -X

　　3.6 按数字排序        ：#ls -lv

　　-t 以时刻排序。

　　-r 对目录反向排序

　　-f -U 对输出的文件不排序。

　　-X 以文件的扩展名(最终一个 . 后的字符)排序。

　　-S 以文件巨细排序。

　　-u 以文件前次被拜访的时刻排序。

　　-n 用数字的 UID,GID 替代称号。

　　-o 显现文件的除组信息外的具体信息。

　　-p -F 在每个文件名后附上一个字符以阐明该文件的类型，“*”表明可执行的一般

　　文件；“/”表明目录；“@”表明符号连接；“|”表明FIFOs；“=”表明套

　　接字(sockets)。

　　-q 用?替代不行输出的字符。

　　。

下面来看看busybox对ls命令的实现

流程比较简单

先看下ls_main

/*----------------------------------------------------------------------*/int ls_main(int argc, char **argv){struct dnode **dnd;struct dnode **dnf;struct dnode **dnp;struct dnode *dn;struct dnode *cur;long opt;int nfiles = 0;int dnfiles;int dndirs;int oi;int ac;int i;char **av;#ifdef CONFIG_FEATURE_AUTOWIDTHchar *tabstops_str = NULL;char *terminal_width_str = NULL;#endif#ifdef CONFIG_FEATURE_LS_COLORchar *color_opt;#endifall_fmt = LIST_SHORT |(ENABLE_FEATURE_LS_SORTFILES * (SORT_NAME | SORT_ORDER_FORWARD));#ifdef CONFIG_FEATURE_AUTOWIDTH/* Obtain the terminal width.  */get_terminal_width_height(STDOUT_FILENO, &terminal_width, NULL);/* Go one less... */terminal_width--;#endif#ifdef CONFIG_FEATURE_LS_COLORbb_applet_long_options = ls_color_opt;#endif/* process options */#ifdef CONFIG_FEATURE_AUTOWIDTHopt = bb_getopt_ulflags(argc, argv, ls_options, &tabstops_str, &terminal_width_str#ifdef CONFIG_FEATURE_LS_COLOR, &color_opt#endif);if (tabstops_str) {tabstops = atoi(tabstops_str);}if (terminal_width_str) {terminal_width = atoi(terminal_width_str);}#elseopt = bb_getopt_ulflags(argc, argv, ls_options#ifdef CONFIG_FEATURE_LS_COLOR, &color_opt#endif);#endiffor (i = 0; opt_flags[i] != (1U<<31); i++) {if (opt & (1 << i)) {unsigned int flags = opt_flags[i];if (flags & LIST_MASK_TRIGGER) {all_fmt &= ~LIST_MASK;}if (flags & STYLE_MASK_TRIGGER) {all_fmt &= ~STYLE_MASK;}if (ENABLE_FEATURE_LS_SORTFILES && (flags & SORT_MASK_TRIGGER)) {all_fmt &= ~SORT_MASK;}if (flags & DISP_MASK_TRIGGER) {all_fmt &= ~DISP_MASK;}if (flags & TIME_MASK) {all_fmt &= ~TIME_MASK;}if (flags & LIST_CONTEXT) {all_fmt |= STYLE_SINGLE;}#ifdef CONFIG_FEATURE_HUMAN_READABLEif (opt == 'l') {all_fmt &= ~LS_DISP_HR;}#endifall_fmt |= flags;}}#ifdef CONFIG_FEATURE_LS_COLOR{/* find color bit value - last position for short getopt */#if CONFIG_FEATURE_LS_COLOR_IS_DEFAULTchar *p;if ((p = getenv ("LS_COLORS")) != NULL &&(*p == '\0' || (strcmp(p, "none") == 0))) {;} else if (isatty(STDOUT_FILENO)) {show_color = 1;}#endifif((opt & (1 << i))) {  /* next flag after short options */if (color_opt == NULL || strcmp("always", color_opt) == 0)show_color = 1;else if (color_opt != NULL && strcmp("never", color_opt) == 0)show_color = 0;else if (color_opt != NULL && strcmp("auto", color_opt) == 0 && isatty(STDOUT_FILENO))show_color = 1;}}#endif/* sort out which command line options take precedence */#ifdef CONFIG_FEATURE_LS_RECURSIVEif (all_fmt & DISP_NOLIST)all_fmt &= ~DISP_RECURSIVE;/* no recurse if listing only dir */#endifif (ENABLE_FEATURE_LS_TIMESTAMPS && ENABLE_FEATURE_LS_SORTFILES) {if (all_fmt & TIME_CHANGE)all_fmt = (all_fmt & ~SORT_MASK) | SORT_CTIME;if (all_fmt & TIME_ACCESS)all_fmt = (all_fmt & ~SORT_MASK) | SORT_ATIME;}if ((all_fmt & STYLE_MASK) != STYLE_LONG) /* only for long list */all_fmt &= ~(LIST_ID_NUMERIC|LIST_FULLTIME|LIST_ID_NAME|LIST_ID_NUMERIC);#ifdef CONFIG_FEATURE_LS_USERNAMEif ((all_fmt & STYLE_MASK) == STYLE_LONG && (all_fmt & LIST_ID_NUMERIC))all_fmt &= ~LIST_ID_NAME;/* don't list names if numeric uid */#endif/* choose a display format */if (!(all_fmt & STYLE_MASK))all_fmt |= (isatty(STDOUT_FILENO) ? STYLE_COLUMNS : STYLE_SINGLE);/* * when there are no cmd line args we have to supply a default "." arg. * we will create a second argv array, "av" that will hold either * our created "." arg, or the real cmd line args.  The av array * just holds the pointers- we don't move the date the pointers * point to. */ac = argc - optind;/* how many cmd line args are left */if (ac < 1) {static const char * const dotdir[] = { "." };av = (char **) dotdir;ac = 1;} else {av = argv + optind;}/* now, everything is in the av array */if (ac > 1)all_fmt |= DISP_DIRNAME;/* 2 or more items? label directories *//* stuff the command line file names into an dnode array */dn = NULL;for (oi = 0; oi < ac; oi++) {cur = my_stat(av[oi], av[oi]);if (!cur)continue;cur->allocated = 0;cur->next = dn;dn = cur;nfiles++;}/* now that we know how many files there are   ** allocate memory for an array to hold dnode pointers */dnp = dnalloc(nfiles);for (i = 0, cur = dn; i < nfiles; i++) {dnp[i] = cur;/* save pointer to node in array */cur = cur->next;}if (all_fmt & DISP_NOLIST) {//仅显示指定目录信息,不显示子目录if (ENABLE_FEATURE_LS_SORTFILES) dnsort(dnp, nfiles);if (nfiles > 0)showfiles(dnp, nfiles);} else {dnd = splitdnarray(dnp, nfiles, SPLIT_DIR);dnf = splitdnarray(dnp, nfiles, SPLIT_FILE);dndirs = countdirs(dnp, nfiles);dnfiles = nfiles - dndirs;if (dnfiles > 0) {if (ENABLE_FEATURE_LS_SORTFILES) dnsort(dnf, dnfiles);showfiles(dnf, dnfiles);if (ENABLE_FEATURE_CLEAN_UP)free(dnf);}if (dndirs > 0) {if (ENABLE_FEATURE_LS_SORTFILES) dnsort(dnd, dndirs);showdirs(dnd, dndirs, dnfiles == 0);if (ENABLE_FEATURE_CLEAN_UP)free(dnd);}}if (ENABLE_FEATURE_CLEAN_UP)dfree(dnp, nfiles);return (status);}

ls_main也是先对参数进行解析，然后看是否需要递归显示该目录下的所以字目录，我们这里看下只显示该目录下的文件，而不显示他们的字目录，调用showfiles

/*----------------------------------------------------------------------*/static void showfiles(struct dnode **dn, int nfiles){int i, ncols, nrows, row, nc;int column = 0;int nexttab = 0;int column_width = 0; /* for STYLE_LONG and STYLE_SINGLE not used */if (dn == NULL || nfiles < 1)return;if (all_fmt & STYLE_ONE_RECORD_FLAG) {//格式的一些判断ncols = 1;} else {/* find the longest file name-  use that as the column width */for (i = 0; i < nfiles; i++) {int len = strlen(dn[i]->name) +#ifdef CONFIG_SELINUX((all_fmt & LIST_CONTEXT) ? 33 : 0) +#endif((all_fmt & LIST_INO) ? 8 : 0) +((all_fmt & LIST_BLOCKS) ? 5 : 0);if (column_width < len)column_width = len;}column_width += tabstops;ncols = (int) (terminal_width / column_width);}if (ncols > 1) {nrows = nfiles / ncols;if ((nrows * ncols) < nfiles)nrows++;                /* round up fractionals */} else {nrows = nfiles;ncols = 1;}for (row = 0; row < nrows; row++) {for (nc = 0; nc < ncols; nc++) {/* reach into the array based on the column and row */i = (nc * nrows) + row;/* assume display by column */if (all_fmt & DISP_ROWS)i = (row * ncols) + nc;/* display across row */if (i < nfiles) {if (column > 0) {nexttab -= column;while (nexttab--) {putchar(' ');column++;}}nexttab = column + column_width;column += list_single(dn[i]);//显示一行信息}}putchar('\n');column = 0;}}

Showfiles先对显示中间的一些空格,TAB长度做一些判断，然后调用list_single显示一行信息。

/*----------------------------------------------------------------------*/static int list_single(struct dnode *dn){int i, column = 0;#ifdef CONFIG_FEATURE_LS_USERNAMEchar scratch[16];#endif#ifdef CONFIG_FEATURE_LS_TIMESTAMPSchar *filetime;time_t ttime, age;#endif#if defined(CONFIG_FEATURE_LS_FILETYPES) || defined (CONFIG_FEATURE_LS_COLOR)struct stat info;char append;#endifif (dn->fullname == NULL)return (0);#ifdef CONFIG_FEATURE_LS_TIMESTAMPSttime = dn->dstat.st_mtime;/* the default time */if (all_fmt & TIME_ACCESS)ttime = dn->dstat.st_atime;if (all_fmt & TIME_CHANGE)ttime = dn->dstat.st_ctime;filetime = ctime(&ttime);#endif#ifdef CONFIG_FEATURE_LS_FILETYPESappend = append_char(dn->dstat.st_mode);#endiffor (i = 0; i <= 31; i++) {switch (all_fmt & (1 << i)) {case LIST_INO:column += printf("%7ld ", (long int) dn->dstat.st_ino);break;case LIST_BLOCKS:#if _FILE_OFFSET_BITS == 64column += printf("%4lld ", (long long)dn->dstat.st_blocks >> 1);#elsecolumn += printf("%4ld ", dn->dstat.st_blocks >> 1);#endifbreak;case LIST_MODEBITS:column += printf("%-10s ", (char *) bb_mode_string(dn->dstat.st_mode));break;case LIST_NLINKS:column += printf("%4ld ", (long) dn->dstat.st_nlink);break;case LIST_ID_NAME://显示用户名#ifdef CONFIG_FEATURE_LS_USERNAMEbb_getpwuid(scratch, dn->dstat.st_uid, sizeof(scratch));printf("%-8.8s ", scratch);bb_getgrgid(scratch, dn->dstat.st_gid, sizeof(scratch));printf("%-8.8s", scratch);column += 17;break;#endifcase LIST_ID_NUMERIC:column += printf("%-8d %-8d", dn->dstat.st_uid, dn->dstat.st_gid);break;case LIST_SIZE:case LIST_DEV:if (S_ISBLK(dn->dstat.st_mode) || S_ISCHR(dn->dstat.st_mode)) {column += printf("%4d, %3d ", (int) major(dn->dstat.st_rdev),   (int) minor(dn->dstat.st_rdev));} else {#ifdef CONFIG_FEATURE_HUMAN_READABLEif (all_fmt & LS_DISP_HR) {column += printf("%9s ",make_human_readable_str(dn->dstat.st_size, 1, 0));} else#endif{#if _FILE_OFFSET_BITS == 64column += printf("%9lld ", (long long) dn->dstat.st_size);#elsecolumn += printf("%9ld ", dn->dstat.st_size);#endif}}break;#ifdef CONFIG_FEATURE_LS_TIMESTAMPScase LIST_FULLTIME:printf("%24.24s ", filetime);column += 25;break;case LIST_DATE_TIME:if ((all_fmt & LIST_FULLTIME) == 0) {age = time(NULL) - ttime;printf("%6.6s ", filetime + 4);if (age < 3600L * 24 * 365 / 2 && age > -15 * 60) {/* hh:mm if less than 6 months old */printf("%5.5s ", filetime + 11);} else {printf(" %4.4s ", filetime + 20);}column += 13;}break;#endif#ifdef CONFIG_SELINUXcase LIST_CONTEXT:{char context[80];int len = 0;if (dn->sid) {  /*  I assume sid initilized with NULL  */  len = strlen(dn->sid)+1;  safe_strncpy(context, dn->sid, len);  freecon(dn->sid);}else {  safe_strncpy(context, "unknown", 8);}printf("%-32s ", context);column += MAX(33, len);}break;#endifcase LIST_FILENAME:#ifdef CONFIG_FEATURE_LS_COLORerrno = 0;if (show_color && !lstat(dn->fullname, &info)) {printf("\033[%d;%dm", bgcolor(info.st_mode),   fgcolor(info.st_mode));}#endifcolumn += printf("%s", dn->name);#ifdef CONFIG_FEATURE_LS_COLORif (show_color) {printf("\033[0m");}#endifbreak;case LIST_SYMLINK:if (S_ISLNK(dn->dstat.st_mode)) {char *lpath = xreadlink(dn->fullname);if (lpath) {printf(" -> ");#if defined(CONFIG_FEATURE_LS_FILETYPES) || defined (CONFIG_FEATURE_LS_COLOR)if (!stat(dn->fullname, &info)) {append = append_char(info.st_mode);}#endif#ifdef CONFIG_FEATURE_LS_COLORif (show_color) {errno = 0;printf("\033[%d;%dm", bgcolor(info.st_mode),   fgcolor(info.st_mode));}#endifcolumn += printf("%s", lpath) + 4;#ifdef CONFIG_FEATURE_LS_COLORif (show_color) {printf("\033[0m");}#endiffree(lpath);}}break;#ifdef CONFIG_FEATURE_LS_FILETYPEScase LIST_FILETYPE:if (append != '\0') {printf("%1c", append);column++;}break;#endif}}return column;}

list_single根据all_fmt值(即ls的参数)，显示相关的信息，这里主要看用户名是如何显示的。

这里linux和android的实现是不一样的，因为Android没有/etc/passwd、也就没有办法保存uid和他对应的name，而且在Android上面我们不需要使用adduser去为每个应用新建一个用户的，我们看一下Android里面的用户名是怎么来的。

这是获取用户名的流程，那getgrgid_r是在那实现的呢，没错，是bonic

在\bionic\libc\bionic\Stubs.cpp中

最终是通过print_app_name_from_appid_userid来获取用户名的

static void print_app_name_from_appid_userid(const uid_t appid,    const uid_t userid, char* buffer, const int bufferlen) {    __libc_android_log_print(ANDROID_LOG_ERROR, "leaves app_id_from_name", "leave appid = %d", appid);  if (appid >= AID_ISOLATED_START) {    snprintf(buffer, bufferlen, "u%u_i%u", userid, appid - AID_ISOLATED_START);  } else if (userid == 0 && appid >= AID_SHARED_GID_START) {    snprintf(buffer, bufferlen, "all_a%u", appid - AID_SHARED_GID_START);  } else if (appid < AID_APP) {//小于应用id的起始值    for (size_t n = 0; n < android_id_count; n++) {      if (android_ids[n].aid == appid) {        snprintf(buffer, bufferlen, "u%u_%s", userid, android_ids[n].name);        return;      }    }  } else {    snprintf(buffer, bufferlen, "u%u_a%u", userid, appid - AID_APP);//应用程序的uid name  }   __libc_android_log_print(ANDROID_LOG_ERROR, "leaves app_id_from_name", "leave buffer = %s", buffer);}

从代码中可以看到，应用程序最终的name 都是u +uid + _ + a + appid –AID_APP

如下图：

Uid都是0

 

Linux下面的实现也是类似的，其getpwuid_r是在glic中实现的，这里就没去研究。